The present invention relates to methods and apparatus for printing a graphic product on sheet material in accordance with a printing program and stored data representative of the graphic product, and more particularly to methods and apparatus for printing a wide format multicolor graphic product on a printing sheet, such as a vinyl sheet for use as signage.
Known in the art are thermal printing apparatus for generating signs, designs, characters and other graphic products on a printing sheet in accordance with a printing program and data representative of the graphic product. Typically, a thermal printer interposes a donor sheet that includes donor material and a backing between a thermal printhead and the printing sheet. The thermal printhead includes an array of thermal printing elements. The thermal printhead prints by pressing the donor sheet against the printing sheet and selectively energizing the thermal printing elements of the array, thereby selectively transferring pixels of donor medium from the donor sheet to the printing sheet. Movement of the printing sheet relative to the thermal printhead (or vice versa) while pressing the donor sheet against the printing sheet with the thermal printhead draws fresh donor sheet past the thermal printhead. The printing sheet typically includes a vinyl layer secured to a backing layer by a pressure sensitive adhesive so that after printing the vinyl bearing the graphic product can be cut and stripped from the backing material and affixed to an appropriate sign board or other material for display.
The proper printing of many graphic products, such as commercial artwork or signage, can require high quality print work. Often, it is desired that the final multicolor graphic product be physically large, such as several feet wide by tens of feet long. Typically, existing thermal printers are limited in the width of printing sheet that they can print upon. For example, one popular thermal printer prints on sheets that are one foot wide. Accordingly, the final graphic product is often assembled from separately printed strips of printing sheet that must be secured to the signboard in proper registration with one another. Often, the registration is less than perfect and the quality of the final graphic product suffers, especially when backlit.
Wide format thermal printers are known in the art. For example, one wide format thermal printer currently available can accommodate a printing sheet up to three feet wide and uses four full width (i.e., three feet wide) printheads, each interposing a different color donor sheet between the printhead and the printing sheet. Accordingly, far fewer seams, if any at all, require alignment when creating the sign or other product. Also, the use of four printheads allows faster printing of the multicolor graphic product.
Unfortunately, this type of machine can be expensive to manufacture and to operate. For example, each printhead, at a typical resolution of 300 dpi, includes literally thousands of thermal printing elements, all of which are typically required to have resistances that are within a narrow tolerance range. Such a thermal printhead is difficult and expensive to manufacture, and moreover, burnout of simply a few thermal printing elements can require replacement of the entire printhead. Furthermore, donor sheet is also expensive, and the full-width printing heads can be wasteful of donor sheet when printing certain types of, or certain sections of, graphic products. For example, consider that a single color stripe one inch wide and perhaps a foot long is to be printed in center of the printing sheet. Though the printed object occupies {fraction (1/12)} of a square foot, an area of donor sheet that is three feet wide by one foot long, or three square feet, is transferred past the print head when printing the above object, and hence consumed. The printing of a wide format graphic product that includes a narrow border about the periphery of the printing sheet is another example that typically can be wasteful of donor sheet when printing with the above wide format thermal printer.
Other wide format printers are known in the art, such as wide format ink-jet printers, which can also print in a single pass. However, ink-jet printed multicolor graphic products are typically not stable when exposed to the elements (e.g., wind, sun, rain) or require special post-printing treatment to enhance their stability, adding to the cost and complexity of printing with such apparatus.
Accordingly, it is an object of the present invention to address one or more of the foregoing and other deficiencies and disadvantages of the prior art.
Other objects will in part appear hereinafter and in part be apparent to one of ordinary skill in light of the following disclosure, including the claims.
In one aspect, the invention provides a wide format thermal printer for printing a multicolor graphic product onto a printing sheet in separate color planes and responsive to a controller and machine readable data representative of the graphic product. The wide format thermal printer includes a workbed including a platen and having a worksurface for supporting the printing sheet. The worksurface contains a print axis and printing sheet translation axis perpendicular to the print axis.
The wide format thermal printer also includes a pair of translatable clamps each movable between clamped and unclamped conditions relative to the printing sheet supported on the worksurface, and each extending across the workbed in the direction of the print axis from a first end to second end. The clamps are for translating the printing sheet in the direction of the printing sheet translation axis, and the first ends are mechanically coupled to one another and the second ends are mechanically coupled to one another such that the clamps are substantially fixedly spaced from one another in the direction of the printing sheet translation axis. At least one actuator is coupled to the clamp pair for translating the clamp pair in the direction of the printing sheet translation axis between first and second positions.
Further included is a thermal printhead having an array of thermal printing elements extending parallel to the printing sheet translation axis. The thermal printhead is translatable parallel to the print axis for printing on the printing sheet in print swaths extending parallel to the print axis in an area between the clamps by pressing the donor sheet against the printing sheet and selectively energizing the thermal printing elements.
The wide format thermal printer also includes donor sheet means including a supply shaft for rotationally engaging a supply roll of the donor sheet, a take-up shaft for rotationally engaging a take-up roll for winding thereon donor sheet that has been drawn from the supply roll and interposed between the thermal printhead and the printing sheet, and a take-up motor rotationally coupled to the take-up shaft, the shafts and rolls mounted with the thermal printhead for translation parallel to the print axis therewith. Means for securing the printing sheet to the workbed when printing on the printing sheet and releasing the printing sheet from the workbed when translating the printing sheet are also provided.
According to another aspect, the invention provides a wide format thermal printer for printing a multicolor graphic product onto a printing sheet in separate color planes and responsive to a controller and machine readable data representative of the graphic product. The wide format thermal printer includes a workbed including a platen and having a worksurface for supporting the printing sheet, the worksurface including a print axis and a printing sheet translation axis. Also included are: means for translating the printing sheet along a printing sheet translation axis and means for securing the printing sheet to the workbed when printing on the printing sheet and releasing the printing sheet from the workbed when translating the printing sheet.
Also provided is a printhead carriage including the following: a base structure mounted with the printer for translation in the direction of the print axis; a cantilever arm pivotably mounted at a first end to the base structure for pivoting about an axis generally transverse to the print axis, where the cantilever arm mounts a thermal printhead having an array of thermal printing elements extending parallel to the printing sheet translation axis; a pivot actuator coupled to the base and to the other end of the cantilever arm for selectively pivoting the cantilever arm about the pivot axis for lowering and raising the thermal printhead; donor sheet handling means mounted with the base structure for interposing the donor sheet between the thermal printhead and the printing sheet supported by the worksurface, where the donor sheet handling means includes a supply shaft for engaging a supply roll of the donor sheet, a take-up shaft for engaging a take-up roll of donor sheet that has been interposed between the thermal printhead and the printing sheet, and a take-up motor rotationally coupled to the take-up shaft.
In yet another aspect, the invention provides a wide format thermal printer for printing a multicolor graphic product onto a printing sheet in separate color planes and responsive to a controller and machine readable data representative of the graphic product. The wide format thermal printer includes a workbed including a platen for providing a worksurface for supporting the printing sheet, and the worksurface contains a print axis and printing sheet translation axis perpendicular to the print axis. The wide format thermal printer also includes printing sheet translation means for translating the printing sheet along a printing sheet translation axis.
There is also provided a thermal printhead having an array of thermal printing elements extending parallel to the printing sheet translation axis, and donor sheet apparatus including a take-up shaft coupled to a take-up motor and a supply shaft, where the take-up and supply shafts are for coupling to take-up rolls and supply rolls, respectively, of donor sheet. The take-up motor is for winding the donor sheet on the take-up roll after the donor sheet is drawn from the supply roll and interposed between the thermal printhead and the printing sheet. The thermal printhead is translatable parallel to the print axis for printing on the printing sheet in print swaths extending parallel to the print axis in an area between the clamps by pressing the donor sheet against the printing sheet and selectively energizing the thermal printing elements.
Further included are means for securing the printing sheet to the workbed when printing on the printing sheet and releasing the printing sheet from the workbed when translating the printing sheet, and a controller in communication with the printing sheet translation means, the thermal printhead, the donor sheet means and the means for securing the printing sheet for printing the multicolor graphic product on the printing sheet responsive to the stored data representative of the multicolor graphic product.
The controller includes programming stored in a memory associated therewith for controlling printing sheet translation means to translate the printing sheet in one direction parallel to the printing sheet translation axis between successive print swaths when printing one of the color planes and to translate the printing sheet in the opposite direction parallel to the printing sheet translation axis when printing a different color plane.
In an additional aspect of the invention, there is provided a wide format thermal printer for printing a graphic product onto a printing sheet responsive to machine readable data representative of the graphic product. The wide format thermal printer includes a workbed having a worksurface for supporting the printing sheet and a thermal printhead having an array of thermal printing elements for pressing a donor sheet against the printing sheet for printing on the printing. Also included are printing sheet translation means for translating the printing sheet along a printing sheet translation axis and donor sheet means including first and second shafts for mounting supply and take-up rolls, respectively, of donor sheet. The donor sheet is drawn from the supply roll, interposed between the thermal printhead and the printing sheet for printing therewith, and wound on the take-up roll, and the donor sheet means further includes a take-up motor for coupling to the take-up roll for applying a torque thereto and a brake for applying a braking force to the donor sheet.
Also included is a data transfer element for reading data from a memory element mounted with one of the supply and take-up rolls of donor sheet, and a controller in communication with the printing sheet translation means, the thermal printhead, the data transfer element and the take-up motor for printing the multicolor graphic product on the printing sheet responsive to the stored data representative of the multicolor graphic product.
The controller includes programming stored in a memory associated therewith for reading data characteristic of the donor sheet from the memory element, determining the radius of at least the take-up roll from the read data characteristic of the donor sheet, determining a desired tension to be applied to the donor sheet during printing and energizing the take-up motor responsive to the radius of the take-up roll and the desired tension for applying the desired tension to the donor sheet.
In a further aspect, the invention provides a method of printing with a thermal printer that prints a multicolor graphic product on a printing sheet in each of different color planes responsive to machine readable data representative of the color planes. The method includes the following steps:
A) supporting the printing sheet with a worksurface
B) selecting a supply length of donor sheet corresponding to the color plane to be printed and interposing a section of the supply length between the thermal printhead and the printing sheet, the thermal printhead having an array of thermal printing elements extending parallel to a printing sheet translation axis;
C) printing the color plane on the printing sheet in print swaths extending parallel to a print axis substantially orthogonal to the printing sheet translation axis by repeating the following steps 1) and 2) alternately:
1) translating the printhead parallel to the print axis and selectively energizing the thermal printing elements while pressing the donor sheet against the printing sheet with the thermal printhead so as to draw the donor sheet past the printhead;
2) translating the printing sheet parallel to the translation axis between print swaths; and
D) performing steps A, B, and C for each of the color planes to be printed to print the multicolor graphic product on the printing sheet, wherein when printing at least one of the color planes the printing sheet is translated in the opposite direction parallel to the translation axis between consecutive swaths to that in which it is translated between consecutive swaths when printing a different color plane.
In yet a further additional aspect, the invention provides a method of tensioning donor sheet in a thermal printer wherein the donor sheet is drawn from a supply roll, interposed between a thermal printhead and a printing sheet and wound on a take-up roll. The method includes the following steps:
providing a take-up motor coupled to the take-up roll for providing a rotational torque to the take-up roll responsive to the energization of the take-up motor;
providing a brake coupled to the donor sheet for applying a selected braking force to the donor sheet;
reading data characteristic of the donor sheet from a memory element mounted with one of the supply roll and the take-up roll;
determining a desired tension to be applied to the donor sheet; determining the radius of at least the take-up roll as a function of at least the data characteristic of the donor sheet read from the memory element; and
applying the desired tension to the donor sheet, including the step of selectively energizing the take-up motor as a function of the radius of the take-up roll and the desired tension to be applied to the donor sheet.